Method of making integral external and internal finned tubing



J. 5. R0 5 2,463,997 METHOD OF MAKING I E L EXTERNAL AND INTERNAL FINNED TUBING Filed June 19, 1944 March 8, 1949.

mm .pn IA ,,l .1 v 1 941?? INVENTOR.

- JAMES S.RODGERS ATTORNEYS Patented 'Mar.

METHOD OF MAKING INTEGRAL F ZXTEBNAL AND INTERNAL FINNED TUBING James S. Rodgers, Detroit, Mlch.,. asslgnor to Calumet and Heels Consolidated Copper Company, Calumet; Mieln, a corporation of Michian A I l The invention relates to finned tubing designed for use in heat exchange apparatus and itis the primary objector the invention to obtain a-oonstructionhavlng higher heat exchange efliciency. In one form of finned tubing heretofore manufactured, radially extending helical this are extruded from the peripheral portion of a plain tube; Such construction is high in heat exchange capacity due to the fact that the metal in a structure thus formed has greater thermal conductivity than that in a cast construction. However, the limiting factor is the small areas. of the inner surface of the tube as compared with that of the external fin-surface.

It is the object of the instant invention to increase the emciency of such finned tubing by providing the same with inwardly projecting integral fins so as to greatly increase the area of contact with the fluid medium passing through the tube. However, as heretofore manufactured, the tubing has been supported on a mandrel within the same during the process of forming or extruding thev external helical fins. Consequently, the presence of internal fins might interfere with the use of such a mandrel. On the other hand, if the structure were to be formed by some other process, such as casting, then the thermal conductivity of the metal would be lowered reducing eificiency as a heat exchange medium. a

In view of the conditions-just described, my

. Application June 19, 1944, Serial No. 541,002 i (ores-457.3)

Fig. i is a diagrammatic view illustrating the method of forming the external fins.

As illustrated in Figs. 1 and 2, my improved finned tubing has a body portion A provided with a plurality of radially inwardly projecting and longitudinally extending fins Bwhich are slightly twisted or of helical form. C are the external flns which may be either annular or helical but with a relatively large helix angle. The inner surface of the body portion A of the tubing has depressions A intermediate the fins C which impart a wavy or serpentine form to such surface.

The method of forming such finned tubing comprlsesessentially two steps. In the first stepa tubular blank D is formed by extrusion or other means, said blank having a cylindrical outer surface D and inwardly and longitudinally.

into the peripheral portion of the blank to a invention consists in a process or method by gible resistance to the flow of fluid therethrough.

The invention further consists in a method of imparting a wavy form to the internal surface of the tubing for increasing efllciency in heat exchange. I

The invention further consists in the novel product as hereinafter set forth.

In the drawings:

predetermined depth cutting a groove therein. The" succeeding discs F, F", etc. are progressively increased in width so as to axially compress the metal of the blank therebetween to extrude it radially. For directing the blank into engagement with the rollers it passes through a tubular external guide G. If the blank were not provided with the internal ribs D it would not have 'sufiicdent rigidity to withstand the-radially mward stresses produced by the rollers F. However, the trussing or reinforcement of theseribs will to a great extent resist such stresses while the external fins are being axially compressed and radially extruded. Nevertheless, there will be v a slight inward displacement of the wall of the tubing between the external fins while the Fig. 1 is a central longitudinal section through latter hold the portions in line therewith from such displacement. This will produce the wavy inner surface A previously described.

Dm'ing the formation of the external fins the blank will be subjected by the forming mechanism to certain internal stresseswhich result in a slight twisting about its axis. This will change the shape of the internal fins from a form parallel to the axis of the tubing to a slightly helical form.

It is also possible during the extrusion of the projectinggfins. Y The amount and the direction 0i twisting or these fins can also be controlled so that i! ltis desired to havethe internal fins of a particular helix angle, this may be controlled, first. by'imparting a predetermined helix angle to the extruded blank and, second, by modiiying this through the twisting of the blank which occurs when the external fins are being formed. In other words, it the-helix angle imparted by the external fin forming mechanism is greater than desired, then the blank may be extruded with a negative helix angle and the two operations will give just the angle desired.

WhatIclaimasmyinvention is: In a method of forming finned tubing, includ ing the step or extruding a tubular blank with integral fins and the step of developing by a transverse rolling operation external transversely extending fins from the peripheral portion of said extruded blank and simultaneously imparting a slight twist to the blank and the internal fins thereof; thestep of imparting a predetermined helixangle other than zero to the internal 'internally projecting longitudinally extending I blank to impart-a helical form some 1mm j fins dim; the extrusion of the blank to control the final new: angle or said internal fins at the completion oi' the external fin forming operation.

" JAMES s. RODGERS.

REFERENCES CITED The following references are of record in the file of this patent: f

' UNITED STATES PATENTS Number Name a Date 1,816,159 Smith July 28,1931 1,902,779 Hofiman Mar. 21, 1933 1,909.20! Pallgha May, 16, 1933 1,983,488 Kline Dec. 4, 1931 2,244,800 Pascale 'June 10, 1941 2,281,206 Schoen Apr. 28, 1942 2,281,207 Schoen Apr. 28, 1942 2,322,341 Booth June 22, 1948 L .1 FOREIGN PATENTS Number Country Date 846. Great Britain Feb. .21, 1882 111,528 Australia Sept. 12, 1940 531,503

Germany Aug. 10, 1931 

